This invention relates to graft copolymers as multipurpose additives for lubricating oils and hydrocarbon motor fuels. More particularly, this application relates to graft copolymers, wherein the grafted monomer units are derived from a monomer system comprising maleic acid or anhydride and one or more other monomers copolymerizable therewith, to methods of preparing the graft copolymers, and to lubricating oils and motor fuels containing the graft copolymers.
Internal combustion engine sludge is produced by the oxidative degradation of lubricating oils and by the partial oxidation of motor fuels and byproducts of motor fuel combustion. The partially oxidized byproducts of motor fuel combustion contain reactive intermediates such as aldehydes, acids and hydroxy acids which undergo complex condensation reactions to form insoluble resinous materials known as sludge and varnish. Accordingly, unless the components are dispersed relatively soon after formation, they will settle out of the lubricant, causing filter plugging and sticking of moving parts.
In the past, lubricating oils and hydrocarbon motor fuels have been formulated with several additives to provide a plurality of properties, including improved viscosity-temperature characteristics (viscosity index or "VI"), pour point depressancy, oxidation inhibition, anti-rust and detergency. However, multiple additives add substantially to the cost of a lubricating oil or motor fuel and cause problems of imcompatibility and interaction of the additives. The graft copolymer additives of the present invention combine several of these properties in a single material and therefore provide a significant improvement over mixtures of additives.
While the grafting of polar monomers to polyolefinic backbones to form lubricating oil and motor fuel additives is known, as in U.S. Pat. No. 3,404,091, and the use of maleic anhydrides as a graft monomer is known, as in U.S. Pat. Nos. 3,687,849 and 3,687,905, the products obtained are deficient in various properties and/or are too costly, primarily because insufficient maleic acid or anhydrides is incorporated into the graft copolymer and/or the products contain unduly high levels of byproducts of little or no usefulness, such as homopolymers. Maleic acid or anhydride is particularly desirable as a graft monomer because this monomer is relatively inexpensive and therefore, in theory, is an economical route to incorporation of dispersant nitrogen compounds into polymers by reaction of the nitrogen compounds with the carboxyl groups of the maleic acid or anhydride. However, in practice, maleic acid or anhydride will not polymerize to any substantial extent after grafting and therefore cannot provide the amount of carboxyl functionality required for incorporation of significant amounts of dispersant nitrogen through reaction with carboxyl groups. The graft copolymers of this invention are prepared in a manner which maximizes maleic acid or anhydride incorporation and minimizes byproduct formation.